1. Field of the Invention
The present invention relates to an antifog and antireflection optical element. In particular, the present invention relates to an optical element such as a photographic lens, a projection lens, a filter, and a mirror which is excellent in antifog, antireflection, and weather resistance, or optical equipment such as electrophotographic equipment incorporating such an optical element.
2. Related Background Art
Conventionally, for preventing fog of a lens, a filter, a mirror, and the like, a method of coating a surface with a surfactant is generally conducted. Recently, it is also known that fog is prevented by coating a base such as a lens, a filter, a mirror, or the like with a water-absorbing material instead of a surfactant. Furthermore, conventionally, natural polymers are known as a water-absorbing materials, e.g, starch-based polymers such as a starch-acrylonitrile graft polymer hydrolysate; and cellulose-based polymers such as cellulose-acrylonitrile graft polymer. Also known as water-absorbing material are synthetic polymers, e.g., polyvinyl alcohol-based polymers such as a polyvinyl alcohol cross-linked polymer; acrylic polymers such as a sodium polyacrylate cross-linked substance; polyether-based polymers such as a polyethylene glycol/diacrylate cross-linked polymer, etc.
However, the above-mentioned conventional antifog optical elements have the following problems. First, in the case where a surfactant is used for preventing fog, duration of its effect is very short, and unless the surfactant is applied again within several hours or days, its effect cannot be maintained. Furthermore, in the case where dirt on the surface of an optical element is wiped off with water or the like, a surfactant film is removed, and its effect is lost.
Furthermore, in the case where various water-absorbing materials are applied to form an antifog film for preventing fog, the duration of its effect is remarkably enhanced as compared with the case of using a surfactant. However, according to the study by the inventors of the present invention, the following was found: in the case where the water-absorbing material is used for an antifog film, when a low refractive material layer is coated onto the antifog film so as to obtain an antireflection effect, the antifog characteristic of the antifog film itself tends to be lost. Furthermore, in the case where the thickness of the water absorption film is reduced, and the thickness of an optical film is adjusted to an odd multiple of one-quarter of the wavelength of an antireflection target to obtain an antireflection film, the thickness of the water-absorbing film becomes too small, and sufficient antifog characteristic cannot be obtained.
In order to solve the above-mentioned problem, the inventors of the present invention have proposed in Japanese Patent Application Laid-Open No. 11-109105 that a film having a different refractive index is formed on a water absorption film to form an antireflection film. However, in the above-mentioned antifog and antireflection optical element, the following phenomenon is observed sometimes: when the state of containing water continues, a material in the water absorption film moves, resulting in poor surface precision.
Therefore, with the foregoing in mind, it is an object of the present invention to provide an optical element having both an antifog effect and antireflection characteristic as well as morphological stability, or to provide optical equipment in which moisture condensation or the like does not occur when incorporating the optical element therein.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.
In order to solve the above-mentioned problems, according to a first aspect of the present invention, there is provided an optical element having an antifog characteristic, characterized by comprising: an optical component (including a simple glass substrate etc); and a first water absorption layer containing a water-absorbing polymer which is formed on the optical component, in which the first water absorption layer contains a mixture of a water-absorbing polymer and an inorganic substance.
Also, in the optical element, a rate of the inorganic substance mixed in the first water absorption layer is 5 to 60 w % (% by weight).
Also, a rate of the inorganic substance mixed in the first water absorption layer is 15 to 50 w % (% by weight).
Also, the inorganic substance is inorganic particles.
Also, the inorganic substance is SiO2.
Also, the inorganic particles are mixed in the first water absorption layer as they are, that is, in the form of particles.
Also, the inorganic particles are contained in the first water absorption layer as particles having a diameter of 5 nm to 20 nm.
Also, a thickness of the first water absorption layer is 1 xcexcm to 20 xcexcm.
Also, there is provided an optical element characterized by further comprising a high refractive layer formed on the first water absorption layer, and a second water absorption layer containing a water-absorbing polymer which is formed on the high refractive layer.
Also, the second water absorption layer contains the inorganic substance.
Also, a thickness of the second water absorption layer is less than 1 xcexcm.
Also, a thickness of the second water absorption layer is less than 200 xcexcm.
Also, a plurality of antireflection layers, each consisting of the high refractive layer and the second water absorption layer that are integrally formed, may be stacked to constitute an optical element.
Also, a water-absorbing polymer in at least one of the first water absorption layer and the second water absorption layer is a polyacrylic acid or polyvinyl alcohol.
Also, an optical element is one selected from the group consisting of a filter for a photographic lens or a projection lens, a mirror, and a lens.
Also, the optical element has antireflection characteristic.
Also, the optical equipment has the above optical component.
Also, the optical element is exposed to the outside.
Also, the optical equipment is an image pickup apparatus including an image pickup optical system and a finder optical system, the finder optical system including the optical element.
Also, the optical element is an eyepiece of the finder optical system.